Novel Tools for Genetic Manipulation of Follicle Stem Cells in the Drosophila Ovary Reveal an Integrin-Dependent Transition from Quiescence to Proliferation

Abstract

In many tissues, the presence of stem cells is inferred by the capacity of the tissue to maintain homeostasis and undergo repair after injury. Isolation of self-renewing cells with the ability to generate the full array of cells within a given tissue strongly supports this idea, but the identification and genetic manipulation of individual stem cells within their niche remain a challenge. Here we present novel methods for marking and genetically altering epithelial follicle stem cells (FSCs) within the Drosophila ovary. Using these new tools, we define a sequential multistep process that comprises transitioning of FSCs from quiescence to proliferation. We further demonstrate that integrins are cell-autonomously required within FSCs to provide directional signals that are necessary at each step of this process. These methods may be used to define precise roles for specific genes in the sequential events that occur during FSC division after a period of quiescence.

Sorting Out Identities: An Educational Primer for Use with “Novel Tools for Genetic Manipulation of Follicle Stem Cells in the Drosophila Ovary Reveal an Integrin-Dependent Transition from Quiescence to Proliferation”

“…The GAL4/UAS system has played an important role in research using many model organisms. Hartman et al (2015) utilized an extensive collection of fly lines from multiple sources with GAL4 is expressed in a specific cell type based on the enhancer/promoter element located near the GAL4 insertion site in the genome. Flies containing this insertion are mated to another fly line that contains a target gene downstream of the UAS element.…”

“…As one of the authors' goals was to examine the shape, or morphology, of cells, it was disadvantageous to have adjacent cells labeled as they become difficult to distinguish. Therefore, Hartman et al (2015) further refined the MARCM technique to control when labeled daughter cells are generated. Following the induction of clones by heat shock, they allowed the labeled daughter cells to differentiate into follicle cells and exit the germarium.…”

“…However, a significant limitation to these studies has been a lack of ways to effectively distinguish the FSCs from other somatic cell populations within the gonad and to manipulate gene expression within specific cell types. Hartman et al (2015) set out to alleviate this difficulty by identifying genetic elements that regulate gene expression in different cell populations in the ovary, specifically the FSCs. They then can label and manipulate the FSCs and probe the role of specific genes in FSCs.…”

“…Hartman et al (2015) utilized these tools to examine gene expression in the adult ovary. Drosophila have two ovaries, each composed of 15-20 ovarioles ( Figure 1; reviewed in Spradling 1993).…”

“…Studies of the characteristics and functions of FSCs have been hampered by a lack of methods for specifically marking these cells. Therefore, Hartman et al (2015) set out to identify additional tools that can be used to distinguish FSCs from other cell populations within the ovary and to demonstrate how these tools can be used to study the function of specific genes in the FSCs.…”